1996 Volvo Penta 7.4GL overheated

[danyus1]

I was out over the weekend and my motor overheated causing the rubber exhaust hoses to melt on the Y. I was towed in and got the boat on the trailer. I've checked the oil and not seeing any milky oil. My question is what else do I need to do to determine if there was any other damage done to the motor? I plan to replace the impeller, all exhaust hoses, pull the riser and check them, and flush the whole system, hoping it will solve the heating issue. Is that my best bet, or do I need to have the motor torn down for further damage? Any advice would be great. I'm hoping I didn't destroy the engine!

 

[tpenfield]

Doing the cooling system maintenance as you described is your best approach. What would indicate to you that an engine tear-down would be warranted? It is a 7.4 (454) which are pretty robust engines.

For how long was it run in an overheated fashion? do you have a temperature gauge? If so, what did it read. Did any temperature alarm sound?

 

[danyus1]

It did not run hot for a very long time, as the trip back to the marina was only 15 mins, and I made it about 1/2 way to the marina. The engine shut itself off, but not before the damage to the rubber hoses were toasted. The alarm came on after the engine was in failure mode (no advanced warning). I looked at the temp gauge and I was around 240 at the time it shut down. I never tried starting it back up until the following day, which it turned over fine and started on first crank. I just wanted to be safe than sorry. If there were other clues I'm missing.

 

[Scott Danforth]

do a compression check.

240 is already past the steam phase as in no cooling water flow

when was the last time you replaced the raw water impeller?

 

[tpenfield]

Yes, to me 240 degrees says not paying attention or running it past being hot.

Agree with Scott regarding compression test. Maybe even a cylinder leak test.

 

[Scott Danforth]

BTW, the 95mm rubber exhaust hose is quite expensive. and no, the standard 4" stuff wont fit.

 

[danyus1]

I changed the impeller 2 years ago. After taking boat out of water it's apparent we hit a sand bar or something that caused damage to the outer prop. My parts manual calls for the 4" part #? I looked at the 95mm and my hoses do not look like those.

 

[Lou C]

Before you run it in the water again check for water in the oil (look inside the valve cover where it shows up before the dipstick) and do a compression test. When you do the comp test look for water coming out of the cyls. This would be suggestive of a blown head gasket (as is water in the oil) or a cracked head, either or both of which are common with severe overheats. You might get lucky or wind up needing a top end overhaul. Low comp test results on 2 adjacent cyls is also a classic sign of a blown HG. If comp test results are good, if no water in the oil, and no water in cyls, it may be OK. I had this happen to mine 5 years ago and it ran great for 2 more seasons and then blew both head gaskets at the end of the 3rd season after the overheat. Tear down revealed both head gaskets had blown putting water in one cyl, a mist of water in the other and both cyl heads had cracks in the center cyls exhaust seats. Two re-man heads and new gaskets and its up and running again....

https://www.dropbox.com/s/ik5tcwbz2pl1k0u/Holley 4160.MOV?dl=0

 

[USA_boater]

I overheated a 4.0 Jeep and a 5.9 dodge magnum, ran them both with no coolant and didn't know it...one had synthetic oil and one used syn-blend; I think that helped a lot to save the bearings in such heat. Both were fine after I fixed the broken radiators and changed the oil...I bet you're okay, may have sucked some life out of that motor but I bet it isn't bad enough to need an overhaul...on some engines not so much, but these cast iron American push rod motors are robust as mentioned. I'd do a compression test too; run some Engine Restore through it if you really do have some uneven cylinders...run it till it quits and then rebuild later.

 

[danyus1]

Thanks everyone. I'll update after I get it all back together. I found the issue. The oil cooler end cap came off! I started going through the cooling system and could feel the end cap of the oil cooler wiggley with touch. I pulled the cooler off and sure enough the one end just came off. Hopefully I'll be ok once I get it all put back together!

 

[danyus1]

Did the compression test my lowest was 125 and the highest was 155. So looks like I’m getting good compression. Going to put it back together this week and take it back to the lake for the weekend.